Absorbent articles

ABSTRACT

An absorbent article containing a composite mixture of absorbent macroporous particles and binder particles. Preferably, the absorbent macroporous particles are those having a macroporous structure which allow for the rapid flow of liquid therein, e.g., aerogels, xerogels, cryogels, or mixtures thereof. The absorbent articles produced thereby are preferably thin and lightweight, but maintain an ample rate of absorption allowing for a more rapid uptake of higher volumes of liquids.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of co-pending U.S.patent application Ser. No. 09/358,183, filed Jul. 20, 1999, which is acontinuation-in-part of U.S. patent application Ser. No. 08/903,395,filed Jul. 22, 1997, that issued as U.S. Pat. No. 6,077,588, which is adivision of U.S. patent application Ser. No. 08/813,055, filed Mar. 7,1997, that issued as U.S. Pat. No. 5,792,513.

BACKGROUND OF THE INVENTION

[0002] I. Field of the Invention

[0003] The present invention relates generally to absorbent articles.Particularly, the present invention relates to absorbent articlescontaining macroporous absorbent materials that provide quick absorptionand subsequent containment of liquid. More particularly, the presentinvention relates to absorbent articles containing aerogels.

[0004] II. Description of the Prior Art

[0005] It is often desirable to impregnate, cover, or otherwise treat abase material with an absorbent or adsorbent material to form anabsorbent article. Examples are found in children's diapers, adultincontinence products, and feminine hygiene products. Other examplesinclude coated paper tissues, toweling, and surgical bandages.

[0006] The active adsorbent or absorbent materials used to coat a basematerial may be fibrous, particulate or both. Fluff pulp is a fibrousabsorbent well known in the art. However, fluff pulp fibers have limitedabsorption capacity and as such, do not always meet the expectations ofnormal use. In addition, fluff pulp fibers are heavy and bulky, andimpart these characteristics into products that contain fluff pulpfibers.

[0007] Super adsorbent polymers (hereinafter SAP) in powdered orgranular form provide enhanced absorptive capacity over traditionalfluff pulp when used alone, or when used in combination with fluff pulpfiber. However, SAP particles that are not well dispersed within anabsorbent product undergo a 1t phenomenon known as “gelling” or “gelblocking”.

[0008] Contact of SAP with liquid causes SAP to swell. Upon contact withliquid, SAP polymer particles in close proximity coalesce to create anSAP gel of limited permeability. Once formed, the SAP gel preventsutilization of underlying absorbent by blocking access thereto.

[0009] The effect of SAP gelling on absorption is of particular concernwhen the absorbent is used in combination with fluff pulp fibers. Thisproblem is made worse by the well-known and often practiced method ofbonding a high percentage of SAP particles directly to the fiberscontained in the absorbent article.

[0010] In light of the foregoing, there exists a need for improvedabsorbent articles that are thin, light weight and effective. Stillfurther, there exists a need for adsorbent and absorbent articles freeof fluff pulp fibers, having both internal porosity suitable for bulkabsorption and subsequent containment of liquid.

SUMMARY OF THE INVENTION

[0011] The present invention describes an absorbent article comprising afirst substrate and a laminate, wherein the laminate comprises a mixtureof binder particles and absorbent macroporous particles.

[0012] In addition, the present invention includes the above absorbentarticle, wherein the binder particles are on average smaller than theabsorbent macroporous particles.

[0013] Furthermore, the present invention includes the above absorbentarticle, wherein at least some of the absorbent macroporous particlesare coalesced by the binder particles to each other, to the firstsubstrate, or to both each other and to the first substrate.

[0014] The present invention also includes the above absorbent articlefurther comprising a second substrate on the laminate, optionallywherein at least some of the absorbent macroporous particles arecoalesced or fused by the binder particles to the second substrate, andsaid laminate is in-between the first substrate and the secondsubstrate.

[0015] The present invention also describes an absorbent article,wherein the absorbent macroporous particles are produced by a processcomprising the steps of forming a liquid-containing gel, and thenremoving the liquid from the gel in a way sufficient to produceabsorbent macroporous particles.

[0016] This invention will be discussed in greater detail in thedescription that follows. Additional advantages of the invention willbecome apparent from this discussion, together with accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a side plan-view of the adsorbent media of the presentinvention; and

[0018]FIG. 2 is a schematic diagram illustrating an apparatus for thepractice of the method of this invention.

DETAILED DESCRIPTION OF THE INVENTION

[0019] Referring to the drawings and, in particular, FIG. 1, there isprovided an absorbent article generally indicated as 1. Relatedabsorbent articles and the methods for producing them are also describedin U.S. Pat. Nos. 6,077,588 and 5,792,513, which are incorporated hereinby reference.

[0020] Absorbent article 1 has a first substrate 6 and optionally asecond substrate sometimes referred to as a covering layer or top sheet7. First substrate 6 and second substrate 7 may be formed of variousmaterials depending upon the intended application, and need not beformed of the same or similar material within one composite. By way ofexample only, substrates 6 and/or 7 may be permeable materials such asnon-woven fibrous webs, e.g., spun bonded, melt blown or cardedmaterials composed of polyester or polyolefinic fibers. The substratesmay also be formed from woven materials. Substrates 6 and/or 7 mayoptionally be formed wholly or in part from cellulosic materialsincluding tissue or towel stock. In the alternative, substrates 6 and/or7 may be semi-permeable to liquids, e.g., a membrane, or a porouspolymeric film, or can be impermeable to liquids, such as, for example,a plastic film.

[0021] The particular material selected for first substrate 6 and/orsecond substrate 7 can effect the kinetics of absorption of absorbentarticle 1. For example, first substrate 6 and/or second substrate 7 canmodify the mean pore size, the overall porosity, and permeability of theabsorbent article. They can also provide supplemental absorption,improve tensile strength, flexibility, pleatability, effect wicking andeffect fluid distribution within absorbent article 1.

[0022] Coalesced with first substrate 6, and optionally with secondsubstrate 7, is a laminate indicated generally as 2. Laminate 2 iscomprised of absorbent macroporous particles 3 and binder particles 4.The binder particles 4 coalesce at least some of the absorbentmacroporous particles 3. An amount of binder particles 4 also coalesceat least some of the absorbent macroporous particles 3 to substrate 6,and optionally to substrate 7, or to both substrates 6 and 7.

[0023] The size distribution of the absorbent macroporous particles 3 istypically from about 5 microns to about 5000 microns, preferably fromabout 140 microns to about 865 microns.

[0024] Any suitable binder material may be employed in this invention.Materials suitable for forming binder particles 4 include, but are notlimited to: thermoplastic and/or thermosetting binders. Preferred bindermaterials are hydrophobic, and include, polyethylene, polypropylene,poly (ethylene vinyl acetate), and nylon.

[0025] Binder particles 4 are on average smaller than the absorbentmacroporous particles 3, generally having a size from about 0.1 micronsto about 100 microns. Preferably, binder particles 4 are 4 to 25 timessmaller in size, on average, than absorbent macroporous particles 3.

[0026] Thickness 5 of composite 1 will vary depending on a variety offactors including, the size of absorbent macroporous particles 3, binderparticles 4, and the quantity of particles 3 and 4 per unit area.Thickness 5 of composite 1 is generally about 0.2 mm to about 10 mm,preferably from about 1 mm to about 2 mm.

[0027] Absorbent macroporous particles 3 have large pores that providerapid wicking, quick absorption of liquids, and can hold a large amountof fluid within in the absence of traditional absorbent materials suchas, for example, fluff pulp. As used herein, the terms macropore ormacroporous particle refer to particles having pores of a size fromabout 90 nanometers to about 1,000 nanometers across.

[0028] Absorbent macroporous particles 3 can be produced in severalways. For example, polyethylene beads containing a chemical crosslinkingagent, such as dicumyl peroxide, can be suspended in an aqueous solutionand heated to a suitable temperature to trigger a crosslinking reaction.The resultant crosslinked resin is then impregnated with a hydrocarbonor chlorofluorocarbon blowing agent, such as butane. Drying the resinthrough heating or freeze-drying creates the absorbent macroporousparticles.

[0029] Other forms of absorbent macroporous particles 3 include what aregenerally referred to as aerogels. Aerogels are highly porous materialsand typically have a much lower density than other absorbent materials.As used herein, the term “aerogel” includes any highly porous materialprepared by removing the liquid from a gel, in such a way that anessentially dry absorbent macroporous structure of the gel material isretained.

[0030] It is believed that fluids are quickly drawn into absorbentmacroporous materials, including aerogels, because of the high capillaryattraction created by the large pores of these absorbents. These highcapillary attraction forces are due to the fact that absorbentmacroporous particles provide a combination of high capillary andosmotic force, with channels that are large enough to provide rapidfluid flow. These macropores, however, being small enough to retain theabsorbed fluid, thereby avoiding “rewetting” of the absorbent article 1.

[0031] The term “aerogel” was coined by S. S. Kistler in U.S. Pat. No.2,188,007, which is incorporated herein by reference. Kistler producedaerogels from a variety of compounds including cellulose, collodion,gelatin, albumin, alumina, nickel hydroxide, thoria, titania, stannicoxide, magnesium hydroxide, chromic oxide, pyroxylin and variouscompounds of iron, cobalt, zinc, cadmium, barium, manganese, vanadiumand copper. Kistler's method involved forming an aqueous gel or jellywith a gel material, and then exchanging the water with a solvent,typically alcohol, and then exchanging the alcohol in the gel with ethylether. The ether containing gel was then submerged in the solvent, andthen placed in a pressure vessel. It was then heated under pressure toabove the critical point of the solvent. This step filled the gel withgas instead of liquid. The gaseous ether was then allowed to escape fromthe vessel while maintaining the conditions within the vessel above thecritical temperature of the solvent. The result was an expanded butdried gel of low density. Aerogels produced according to this methodtypically have densities in the range of 0.03 to 0.3 g/cm³.

[0032] Xerogels are a type of aerogel in which the liquid has beenremoved from the gel under supercritical conditions. Hrubesh of TheLawrence Livermore National Laboratory modified the basic technique forforming aerogels by using condensed silica, a base catalyst andsupercritical fluid extraction to achieve silica aerogels having anultra low density of about 0.005 g/cm³ (See, Robert Pool Science, 247(1990), at 807).

[0033] Others have produced aerogels by crosslinking polymeric gelmaterials, such as chitosan. For example, Japanese Patent PublicationNo. 61-133143, published Jun. 20, 1986, and U.S. Pat. No. 4,833,237 toKawamura et al., incorporated herein by reference, both refer tocrosslinked granular bodies derived from a low molecular weight chitosancrosslinked with diisocyanate.

[0034] Cryogels are another form of aerogel in which the liquid isremoved from a frozen gel by sublimation. Cryogels being dried whilefrozen are macropores due to the particles being pre-swollen prior toliquid removal. This greatly enhances the inter-particle diffusivity ofliquids (see U.S. Pat. No. 5,573,994 to Kabra et al.).

[0035]FIG. 2 illustrates an exemplary apparatus used to produce thisinvention. A supply roll 10 provides a first substrate 12. Downstreamfrom supply roll 10 is a knurled roller 13 positioned to receive amixture of absorbent macroporous particles 3 and binder particles 4,generally indicated as mixture 14, from hopper 16. Mixture 14 is appliedto the upper surface of substrate 12 as a continuous coating or,alternatively, as a coating in a specific design including, but notlimited to, stripes.

[0036] Thereafter, substrate 12 containing mixture 14 is passed throughnip 20 between a heated idler roller 22 and a drive roller 24.Alternatively, before being passed through nip 20, substrate 12containing mixture 14, may be preheated by a pre-heater 50 such as, forexample a convection or infrared oven. A pneumatic cylinder 26 isconnected via a rod 28 to the axle of idler roller 22 to maintain adesired pressure on substrate 12 containing mixture 14 within nip 20. Inpassing through pre-heater 50, and over the surface of heated roller 22,mixture 14 is heated to a temperature equal to or greater than thesoftening temperature of binder particles 4, but to a temperature belowthe softening temperature of absorbent macroporous particles 3. Withinnip 20, an amount of binder particles 4 coalesce under pressure with anamount of absorbent macroporous particles 3. An amount of binderparticles 4 may also coalesce with first substrate 12.

[0037] Furthermore, in a preferred embodiment of the present invention,a second supply roll 30 of a second substrate 32, which may be of thesame or may be of a different material from that of substrate 12, isalso passed between nip 20 on the top of mixture 14. An amount of binderparticles 4 may also coalesce with second substrate 32. Upon leaving nip20, binder particles 4 cool and harden. The finished composite 34 thenpasses onto take-up roll 36.

[0038] By suitable selection of: substrate materials 12 and 32, binderparticles 4, absorbent macroporous particles 3, absorbent macroporousparticle 3 to binder particle 4 weight ratios, absolute amounts ofmixture 14 applied to substrate 12 per unit area, binder particle 4size, absorbent macroporous particle 3 size, the ratio of binderparticle 4 size to absorbent macroporous particle 3 size, heatingtemperature, nip pressure and linear speed of first substrate 12, it ispossible to vary the composite depth, average porosity, permeability,tensile strength, flexibility, pleatability, draping ability, wicking,absorption, adsorption, or other attributes of the absorbent macroporouscomposite of the present invention.

[0039] Although the absorbent article of the present invention has beendescribed with respect to one or more particular embodiments, it will beunderstood that other embodiments of the present invention may beemployed without departing from the spirit and scope of the presentinvention. Hence, the present invention is deemed limited only by theappended claims and the reasonable interpretation thereof.

What is claimed is:
 1. An absorbent article comprising: a firstsubstrate and a laminate, wherein said laminate comprises a mixture ofbinder particles and absorbent macroporous particles.
 2. The absorbentarticle of claim 1, wherein said binder particles are on average smallerthan said absorbent macroporous particles.
 3. The absorbent article ofclaim 1, wherein at least some of said absorbent macroporous particlesare coalesced by said binder particles to each other, to said firstsubstrate, or to both each other and to said first substrate.
 4. Theabsorbent article of claim 1, further comprising a second substrate onsaid laminate.
 5. The absorbent article of claim 4, wherein at leastsome of said absorbent macroporous particles are coalesced by saidbinder particles to each other, to said first substrate, to said secondsubstrate, or to any combinations thereof; and, said laminate isin-between said first substrate and said second substrate.
 6. Theabsorbent article of claim 1, wherein said absorbent macroporousparticles are selected from the group consisting of: aerogels, xerogels,cryogels, and a combination thereof.
 7. The absorbent article of claim1, wherein said absorbent macroporous particles have pores having a sizefrom about 90 nm to about 1,000 nm across.
 8. The absorbent article ofclaim 1, wherein said absorbent macroporous particles have a densityfrom about 0.005 g/cm³ to about 0.5 g/cm³.
 9. The absorbent article ofclaim 1, wherein said absorbent macroporous particles were produced by aprocess comprising the steps of: forming liquid-containing gelparticles, and removing said liquid from said gel particles.
 10. Theabsorbent article of claim 9, wherein said liquid-containing gelparticles were formed from a gel material selected from the groupconsisting of: an alkoxysilane, metal oxide, alumina, biopolymer,organic polymer, silica, carbon and a combination thereof.
 11. Theabsorbent article of claim 10, wherein said gel material is crosslinked.12. The absorbent article of claim 1, wherein said absorbent macroporousparticles have an average particle size from about 5 microns to about5,000 microns.
 13. The absorbent article of claim 1, wherein at leastsome of said binder particles are hydrophobic.
 14. The absorbent articleof claim 2, wherein said binder particles are on average about 4 toabout 25 times smaller than said absorbent macroporous particles.
 15. Amethod for absorbing a liquid comprising the step of: contacting anabsorbent article with a liquid, wherein said absorbent articlecomprises a first substrate and a laminate, wherein said laminatecomprises a mixture of binder particles and absorbent macroporousparticles, thereby absorbing said liquid within said absorbentmacroporous particles.
 16. A method of claim 15, wherein said binderparticles are on average smaller than said absorbent macroporousparticles.
 17. A method of claim 15, wherein at least some of saidabsorbent macroporous particles are coalesced by said binder particlesto each other, to said first substrate, or to both each other and tosaid first substrate.
 18. A method of claim 15, further comprising asecond substrate on said laminate.
 19. A method of claim 18, wherein atleast some of said absorbent macroporous particles are coalesced by saidbinder particles to each other, to said first substrate, to said secondsubstrate, or to any combinations thereof; and, said laminate isin-between said first substrate and said second substrate.
 20. A methodof claim 15, wherein said absorbent macroporous particles are selectedfrom the group consisting of: aerogels, xerogels, cryogels, and acombination thereof.
 21. A method of claim 15, wherein said absorbentmacroporous particles have pores having a size from about 90 nm to about1,000 nm across.
 22. The method of claim 15, wherein said absorbentmacroporous particles have a density from about 0.005 g/cm³ to about 0.5g/cm³.
 23. The method of claim 15, wherein said absorbent macroporousparticles were produced by a process comprising the steps of: formingliquid-containing gel particles, and removing said liquid from said gelparticles.
 24. The method of claim 23, wherein said liquid-containinggel particles were formed from a gel material selected from the groupconsisting of: an alkoxysilane, metal oxide, alumina, biopolymer,organic polymer, silica, carbon and a combination thereof.
 25. Themethod of claim 24, wherein said gel material is crosslinked.
 26. Themethod of claim 15, wherein said absorbent macroporous particles have anaverage particle size from about 5 microns to about 5,000 microns. 27.The method of claim 15, wherein at least some of said binder particlesare hydrophobic.
 28. The method of claim 16, wherein said binderparticles are on average about 4 to about 25 times smaller than saidabsorbent macroporous particles.